1. Field of the Invention
The present invention relates to optical devices, and more particularly to a laser beam scanning optical device for deflecting a laser beam, as modulated in accordance with image data, by deflecting means to cause the beam to scan a photosensitive member to form images thereon.
2. Description of the Related Art
Various optical elements, such as f.THETA. lenses and reflecting mirrors, which are made of resin have been developed in recent years for use in the laser beam scanning optical device to be incorporated into laser printers, facsimile systems, copying machines and the like for image writing because optical elements of resin can be produced in quantities with a specified quality.
However, resin optical elements are prone to deformation or distortion due to variations in the ambient conditions (temperature and humidity) and therefore have the problem that the image forming position of the beam alters with respect to the main scanning direction and subscanning direction. Various structures of simple construction have already been proposed for accurately fixing resin optical elements in position within optical devices. For example, Japanese Laid-Open Patent Application No. 63-157116 discloses an optical device wherein an optical element of resin is positioned in place at its opposite ends with a force parallel to the optical axis and has it central portion placed in position longitudinally and transversely of the device. The conventional structures nevertheless require a large number of components or are unsatisfactory in distortion correcting effect, and still remain to be improved.